7-1 Rocks And Weathering

WEATHERING AND SOIL FORMATION Chapter 7

ROCKS AND WEATHERING Chapter 7 Section 1

Effects of Weathering  Weathering is the process that breaks down rock and other substances at Earth’s surface  Heat, cold, water, and ice all contribute to weathering  Oxygen and Carbon Dioxide also contribute  Forces of weathering break rocks into smaller and smaller pieces  Erosion is the movement of rock particles by wind, water, ice, or gravity

What is the difference between weathering and erosion?  Weathering is the process the process that breaks down rock and other materials at Earth’s surface, while erosion is the movement of rock particles by wind, water, ice, or gravity

Mechanical Weathering  Mechanical Weathering- type of weathering in which rock is physically broken into smaller pieces  Mechanical weathering breaks rock into pieces by freezing and thawing, release of pressure, growth of plants, actions of animals, and abrasion  Abrasion- the grinding away of rock by rock particles carried by water, ice, wind, or gravity  Mechanical weathering works slowly over time and can wear away whole mountains  Ice wedging- frozen wedges of ice in rocks widen and deepen cracks

Chemical Weathering  Chemical weathering- process that breaks down rock through chemical changes  Agents of chemical weathering include water, oxygen, carbon dioxide, living organisms, and acid rain  Chemical weathering creates holes or soft spots in rock, and rocks break apart more easily

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Water

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Water is the most important agent of chemical weathering

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Water dissolves rocks

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Carbo n Dioxide CO2 disso lve s in rainwate r  and fo rms c arbo nic   ac id

Carbo nic  ac id e asily  we athe rs marble  and  Ac id Rain lime sto ne

Oxygen in the air combines with iron causing oxidation

Living  Organisms Ro o ts o f o rganisms push  into  c rac ks in ro c ks

Plants ro o ts pro duc e   we ak acids that  slo wly disso lve  ro ck Lic he ns­ plant like   o rganisms that gro w  o n ro c ks­ also  pro duc e   we ak ac ids

Wate r is the  mo st  impo rtant age nt o f  c he mic al we athe ring Wate r disso lve s ro c ks

Oxygen

Lichen

Rate of Weathering 

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Type of Rock

The minerals that make up the rock determine how fast it weathers Rocks that dissolve easily in water weather more quickly Permeable- a material is fully of tiny, connected air spaces that allow water to seep through it Permeable rock weathers at a fast rate

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Climate

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Climate- the average weather conditions in an area

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Chemical and mechanical weathering occur faster in wet climates

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Rainfall provides the water needed for chemical changes as well as for freezing and thawing

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Chemical reactions occur faster at higher temperatures

Review  1. What factors cause mechanical weathering? 

Freezing and thawing, heating and cooling, growth of plants, actions of animals, and abrasion

 2. Describe three causes of chemical weathering. 

Water that dissolves rocks, oxygen causes oxidation, carbon dioxide dissolves in rainwater, living organisms, and acid rain

 3. What factors affect the rate of weathering? 

Type of rock and climate

 4. Explain why chemical weathering occurs faster in hot, wet climates than in cool, dry climates. 

Rainfall provides the water needed for chemical